1. Field of the Invention
The field of the invention is indwelling stents which aid in the drainage of fluids within the body.
2. Description of the Prior Art
A number of various stents have been devised which are designed to aid in the drainage of fluids within the body. It is generally desirable that a stent being implanted for this purpose be easily implantable, that it maintain patency of the duct and its position within the duct after implantation, that reflux or backflow through the duct be avoided, and that the stent be easily removable.
Stents have been designed in a wide variety of shapes and sizes to effectuate these general requirements. One such example is shown by U.S. Pat. No. 5,052,998 to Zimmon which discloses an indwelling stent having flaps at its inflow end and a pigtail configuration at its outflow end to facilitate anchoring of the stent within the duct to be drained, and also has a series of drainage holes along its length to facilitate drainage. Other stents, mentioned in the Zimmon patent, have commonly employed double flaps, or wings, or have incorporated pigtails on both ends, to hold the stent in place. Prior art stents have been provided both with and without the drainage holes shown in the Zimmon patent.
Reflux is the condition where fluids and/or debris are drawn backwardly up into the duct to be drained. This is undesirable in that it is counterproductive to the purpose of the stent being implanted to drain the duct. Reflux of debris into the stent can also potentially occlude the implanted stent within the duct, which can potentially cause severe aggravation to the condition being treated. Reflux is normally prevented by the functioning of a sphincter located where the duct exits into its receiving organ, however this sphincter operation is inhibited by the placement of an indwelling stent which acts to maintain the patency of the sphincter as well as the duct being drained.
To prevent reflux, U.S. Pat. No. 5,019,102 to Hoene discloses a stent with a dynamic hood-valve at the vesical end of the stent, located within the receiving organ at the downflow end of the obstructed duct. The hood-valve is comprised of a hood-shaped plastic foil that is attached to and partially surrounds the vesical end opening. A reflux pressure causes the hood-valve to fold over to close the vesical opening, thereby preventing retrograde flow from occurring.
Some stents have been devised which terminate within the duct to be drained to allow for normal sphincter operation. U.S. Pat. No. 4,955,859 to Zilber is one such example which suggests the use of a ureteral stent which terminates within the urethra to allow for the normal operation of the external sphincter in order to prevent incontinence.
It is known in the prior art to incorporate means for facilitating the removal of an indwelling stent from the body. U.S. Pat. No. 4,671,795 to Mulchin discloses one such example of an indwelling stent which has a suture attached to its end which extends out of the body and is tied to a button outside the body. The button prevents upward migration and may be pulled to remove the stent from the body. U.S. Pat. No. 4,913,683 to Gregory is another reference disclosing a stent system which utilizes sutures that extend outwardly of the patient and are pulled to remove the stent from the body. Zilber suggests the use of trailing sutures as an aid in the positioning of a stent being implanted. Zimmon suggests drawing the end of a large diameter stent (10 French or greater) to a reduced diameter to facilitate removal [col. 3, lines 52-57] in an effort to compensate for the fact that larger diameter stents are more difficult to grasp and remove.